Surgical lamps fall under the international standard IEC 60601-2-41. This standard determines the requirements of lighting techniques of surgical lamps. Besides the characteristics of the color temperature, the brightness, and limits of radiation, the distribution of brightness in the light field is a characteristic of such surgical lamps. The diminution of brightness when the distance to the center of the light field increases is addressed in the above-noted international standard. The diameter of the light field at which the brightness is 50% of the maximum brightness must be at least half of the diameter of the light field at which the brightness is 10% of the maximum brightness with the lamp body and the operating plane separated by a distance of one meter.
Single reflector lamps are examples of surgical lamps that can fulfill these requirements. In single reflector lamps, the light source is a halogen lamp or a gas discharge lamp, arranged in the focal point of a single reflector having a diameter of about 500 mm to 1000 mm. By displacing the light source along the central axis of the reflector more or less out of the optimal focal point or into the optimal focal point, the diameter of the light field, i.e., the illuminated diameter in the operating field, is enlarged or narrowed. In addition, the focus point is shifted, i.e., the distance between the location which is most brightly illuminated where the reflected light beams intersect and the lamp body of the surgical lamp is changed along the central axis of the lamp body. In these types of lamps, the shape of the light field is circular and not modifiable due to construction.
Multi-reflector light systems constitute another type of construction. In these systems, the surgical lamp usually includes a central spotlight or a central light module, which is rigidly fixed to the lamp body, and several spotlights or light modules, which are annularly arranged about the central spotlight or the central light module. The change of the direction of the light emission of the outer spotlights or light modules is performed by radially pivotable illuminants or reflectors, or the entire spotlights or light modules are radially pivotably adjustable. Thus, the shape of the light field is adjustable such that the light field is circular at an ideal focusing and the light field more closely corresponds to a shape of the arrangement of the outer spotlights when the central axes of the outer spotlights intersect in a point which is not in the operating plane and when the distance between the focus point and the operating plane increases. The distribution of the light intensity changes from a concentric light distribution to a light distribution in which the beams of the outer spotlights are projected in the light field when the distance between the focal point and the operating plane increases.
In surgical lamps of other construction, the light field diameter and the distance of the focal point are not adjustable. In such lamps, the light characteristics are optimally adjusted for one operating point. The shape of the light field is circular. When using multi-reflector lamps, there is the risk that the light field no longer seems homogenous but several light points are projected in the operating area when the distance between the focus point and the operating plane is larger as described with regard to multi-reflector light systems.
The distribution of the light intensity in the light field can be varied by switching on and switching off the illuminants which centrically emit their light to the center of the light field.
For example, EP-A-1 568 034 depicts a surgical lamp with illuminants that can separately be switched on or switched off for enhancing the illumination of the center of the light field. The disclosure EP 1 568 934 depicts a surgical lamp with illuminants in the center of the light field, which can be switched off for avoiding shadowing. EP-A-1 722 157 depicts a surgical lamp with concentric regions, having illuminants that independently can be switched on or be dimmed for avoiding shadowing and optimally illuminating different types of operating wounds (e.g., narrow, deep wounds or widespread wounds). All of these references depict circular light fields at the operating point, i.e., at the optimal distance between the lamp body and the operating plane.
The publication EP-A-1 433 998 discloses a surgical lamp having several light modules which have bundles of light beams, the axes of which are parallel and the light fields of the bundles of light beams partly overlap and result in a shape of the light field which essentially results from the shape of the lamp body. For avoiding shadowing, several light modules are automatically switched off or dimmed. The shape of the light field is unalterable.